In one known type of hydraulically-operated equipment such as travelling equipment and working equipment which are provided in the aforesaid construction machines according to the needs of various kinds of construction work including travelling and working operations, hydraulic pressure for actuating the hydraulic driving mechanism which is driven by hydraulic pressure in the hydraulically-operated equipment is supplied, at a constant supply rate, to the pipeline system of the hydraulic driving mechanism, by means of hydraulic controller valves, hydraulic pumps and similar devices. In other words, the hydraulic driving mechanism is driven by hydraulic pressure, the pressure being supplied at such a constant supply rate that it rises and drops rectilinearly .
Such hydraulically-operated equipment, however, has the following disadvantages: since hydraulic pressure is supplied at a constant supply rate, when a high supply rate is adopted, the hydraulic driving mechanism driven by hydraulic pressure abruptly starts or stops its operation immediately after a dead zone period during which hydraulic pressure starts to rise. As a result of this, the mechanism receives a great shock at the time of start-up and shut-down. On the other hand, when the supply rate is low, the operation of the hydraulic driving mechanism driven by hydraulic pressure becomes sluggish so that there occurs a lag in the operation although the mechanism is free from a shock at the time of its start-up and shut-down.
This is a serious problem, particularly in the use of hydraulically-operated equipment in which more than two operation speed modes, e.g., a high travelling-speed mode can be selected, and low travelling-speed mode; and digging mode (i.e., normal speed mode) and moderating mode (i.e., half speed mode), because a great shock is caused at the time of start-up and shut-down in one mode while in with the other mode an operational lag occurs.
It is therefore a prime object of this invention to provide hydraulically-operated equipment for use in construction machinery which is capable of overcoming the foregoing disadvantages by eliminating a shock at the time of start-up and shut-down and preventing a lag in the operation.